1. Technical Field
The present invention relates generally to silicon-based diodes and in particular to a method of contacting a silicide-based Schottky diode and the diode so formed.
2. Related Art
Referring to FIG. 1, a prior art type silicon-based Schottky barrier diode 100 is shown. Schottky diode 100 includes a silicon Pxe2x88x92 substrate 103 having an N++ portion 104 therein which rises to form cathode area 108, and an N-type section 106 with a P+ guard ring area 112 to form the anode section of the Schottky diode. Insulating layers of silicon oxide 102, 110 may also be provided for masking and definition purposes. In order to form the Schottky barrier, silicide layers 114, 116, respectively, are formed over the cathode and anode sections, including guard ring area 112. Contacts 118 would be formed in subsequent layers for interlayer communication. Further background in the creation of a silicide/silicon Schottky diode is provided in U.S. Pat. No. 4,063,964 to Peressini et al., hereby incorporated by reference.
When contacting a silicide-based Schottky diode, care must be taken to ensure that the formation of a contact to the diode does not disrupt the silicide/silicon interface which forms the Schottky diode. This disruption may occur in a number of ways. First, overetch during contact formation may remove silicide material and change the physical and/or electrical characteristics of the silicide/silicon junction. Second, underetch, which can occur while trying to avoid overetch, can result in residual insulator films at the bottom of the contact. Third, thermal processing during contact formation can result in unwanted metallurgical reactions when dissimilar metals are used for the Schottky diode silicide and the contact (e.g., platinum silicide and titanium/tungsten contacts) or additional silicide formation can occur in the case where the same metal is used for the silicide and contacts (e.g., titanium silicide and titanium/tungsten contacts).
In the three problem situations above, the variability associated with typical manufacturing processes limit the reproducibility and stability of silicide-based Schottky diodes.
Related art processes have attempted to overcome the above problems in a number of ways. For instance, attempts at forming the Schottky diode contact without silicides have been attempted. Unfortunately, this approach has the disadvantage that the Schottky diode contact processing is different than contact processing in the rest of the semiconductor processing technology. Hence, costs and complexity are increased. Another approach has been to form the silicide during the contact metallization. This approach has the disadvantage that the silicide formed is not self-aligned for other devices. Both of the above approaches suffer from the disadvantage that they are incompatible with contact technologies which limit one or more of the dimensions of the contact, such as tungsten stud technologies where the contact is of fixed width in one dimension.
In view of the foregoing, there is a need in the art for a silicide-based Schottky diode formed such that the Schottky diode and, in particular the silicide/silicon interface, is not fouled by contact creating processes.
In a first general aspect of the invention is provided a method of contacting a silicide-based Schottky diode, comprising the steps of: providing a silicide layer over a guard ring area of the Schottky diode; and providing a contact to the silicide layer such that there is a region of the silicide layer between the contact and an internal edge of the guard ring area. Hence, a Schottky diode having a contact to the silicide layer that is bordered by a portion of the silicide layer with respect to an internal edge of the guard ring, is formed. The contact may be bordered or borderless with respect to the external edge of the guard ring. The method may be used in any bi-complementary metal-oxide semiconductor (BiCMOS) Bipolar or CMOS technologies, etc. where diffusions are silicided. In another aspect of the invention is provided an integrated circuit including the above-described Schottky diode and a method of forming an integrated circuit incorporating the processes of forming a Schottky diode described above.
By this invention, the Schottky diode is effectively decoupled from the contact metallurgy. In addition, since the silicide/silicon interface is formed by a high temperature annealing process it is atomically clean and thermally stable. As the contact metallurgy need only touch the silicide over the guard-ring area, the diode characteristics are not influenced by processes used to form the contact. Thus any etch or pre-clean steps may be used when defining the contact and/or any typical thermal anneals may be used to ensure good ohmic contact to the silicide without influencing the diode interface or its electrical characteristics.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.